In practice, a driving torque generated by a drive machine is conducted through a transmission unit to an output means of a vehicle. This operation is made possible in that the motor, the transmission unit and the output means compose a so-called drive train, which is regulated by way of a controlling apparatus.
In order to be able to furnish as many gear stages as possible with the least number of available gear-pairings, the transmission unit is designed as a multi-group transmission which, in turn, consists of a plurality of several transmission groups, which are placed separately in series-aligned arrangement. Where the transmission groups are concerned, it is generally to be understood that such grouping comprises pre-shift gearing, the main transmission and subsequent groups, whereby the latter are subsequently referred to as “range groups”. If the case is that a main transmission of a multi-group transmission is designed as an automatic transmission then a greater driving comfort is acquired if a multiplicity of gear stages are provided. Such an automatic transmission can, for example, possess six gear ratio stages for forward motion and one gear ratio stage for reverse travel.
A range group of a multi-group transmission, described by one input speed of rotation of the range group is always placed in the slow gear stage, where a substantial speed of rotation increase takes place simultaneously. In order to avoid conducting a large start-up moment produced by a range group through the main transmission, range groups are advantageously located following (in the direction of power flow) the main transmission of a multi-group transmission. On this account, a range group of the multi-group transmission is often designed in practice as an auxiliary transmission group or as a planetary transmission group. In such arrangements, a planetary transmission shows itself as a more compact assembly in comparison to an auxiliary transmission group.
A change of a ratio in a range group is executed by a shifting element, whereby shifting can be made between a first ratio “low” and a second ratio “high”. With this arrangement and when in a first selected low gear of the range group and in combination with the main transmission, the driver has a choice of ratios available which are an advantage for operation of a vehicle in a terrain characterized by steep climbs and wherein slow vehicle speeds are acceptable.
The second ratio “high” of the range group is less subject to losses, so that when traveling under normal conditions of terrain and also at higher driving speeds, shifting into the second ratio “high” is to be preferred.
Further, a change of a ratio in a range group activates a considerable jump of ratios in the range group as well as the ratio of the entire multi-group transmission. If an output speed remains essentially the same during the shifting then an extremely large difference in speed of rotation is brought about between the input speed of the motor before the shifting and the input rotational speed of the motor in the “new” ratio of the multi-group transmission, wherein a closable shifting element of the range group is synchronous, relative to the output speed of rotation. In any case, such extreme differences in rotational speeds cause longer time periods for speed equalization, during which time, the driving torque of the motor changes for the very purpose of compensating the differing speed of rotation of the motor. The result is long shifting periods or extended periods of interrupted traction. This becomes a problem since the speed of rotation of the motor must then be reduced.
In order to shorten the shifting periods, a decision was made to the effect that during a change of the ratio of the range group, an identical shift is to be brought about in the main transmission simultaneously. Since this results in a ratio change in the multi-group transmission, the differential of said speeds of rotation is reduced.
However, the disadvantage of this operation is that the torque of the motor is not sufficient to compensate to a different motor speed of rotation within a sufficiently brief time, so that shifting with short-time traction interruption can be achieved. This causes a driving operation up steep inclines to be greatly disadvantaged.
Thus, the purpose of the present invention is to provide a method for the control of a drive train, wherein ratio changes in a range group can be executed with brief traction interruptions.